As a bonding agent for teeth, methylmethacrylate polymer and copolymer of vinyl compounds such as 2,2-bis [4-(2-hydroxy-3-methacryloxypropoxy) phenyl]propane and triethylene glycol dimethacrylate have been used so far, and recently adhesive composites containing 4-methacryloxy-ethyl trimellitic acid anhydride have been prposed and used as a bonding agent for teeth. As the former requires a preliminary treatment of teeth with strong acid due to insufficient adhesive force for teeth, such treatment has a defect of dissolving the surface of teeth more than necessary and also the dental treatment is complicated. The latter exhibits adhesiveness as the result of self curing, but when redox-polymerization catalyst is used as a polymerization catalyst at normal temperature, aromatic tertiary amine which is primarily to be an accelerator in this catalyzer system and the acid anhydride group of 4-methacryloxyethyl trimellitic acid anhydride forms the charge-transfer complex. Consequently the polymerization catalyst cannot perform its original function and polymerization becomes impossible, so the polymerization catalyst at normal temperature used in this adhesion system was practically restricted to tri-n-butylboronoxygen complex. This tri-n-butylboron-oxygen complex has an advantage of offering a strong adhesiveness for a dentin, while it has many disadvantages from the standpoint of dental clinic, i. e. its polymerization reaction is so slow as to take more than ten minutes for final hardening according to circumstances and it is so unstable in the air that its handling is difficult, etc. And yet no anti-irritation and anti-harmfulness properties against tissue, pulp and the like, could be expected from these composites at all.
Irritation and harmfulness against tissue, pulp and the like, often occur in the following case: when the dentin covering the pulp becomes extremely thin due to the depth of cavity, or the affected part is highly sensitive as the result of damage or exposure of the pulp by removing early caries and forming cavity, or when the cavity is directly filled up with composite resin or an usual bonding agent is applied to the cavity before it is filled up with composite resin, though the cavity itself comparatively shallow just as to slightly reach the dentin.
When such cavity was repaired hitherto, a pulp cap was normally used to protect live pulp. When the pulp inflamed because composite resin was filled up without treatment to protect the pulp, the plugging was removed and capping was renewed for later refilling when the inflammation was not serious. However, in case of serious occasions such as purulent inflammation or decay, there was nothing for it but to devitalize the affected tooth by pulpectomy.
Recently an adhesive liner has been invented, which is effective when it is applied to the dentin to form a tunic for protecting teeth against the permeation of external stimulus. Polyacrylic derivative is considered to be the principal component of the adhesive liner, but as this component is as harmful as conventional stuffs when applied to a deep cavity near the pulp or an exposed pulp, it is essential to use the conventional cap together with the adhesive liner for such a symptom and its process is comparatively complex.